libc.info: toupper

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`toupper'--translate characters to upper case

*Synopsis*
     #include <ctype.h>
     int toupper(int C);
     int _toupper(int C);
   *Description*
`toupper' is a macro which converts lower-case characters to upper
case, leaving all other characters unchanged.  It is only defined when
C is an integer in the range `EOF' to `255'.
   You can use a compiled subroutine instead of the macro definition by
undefining this macro using ``#undef toupper''.
   `_toupper' performs the same conversion as `toupper', but should
only be used when C is known to be a lowercase character (`a'-`z').
*Returns*
`toupper' returns the upper-case equivalent of C when it is a character
between `a' and `z', and C otherwise.
   `_toupper' returns the upper-case equivalent of C when it is a
character between `a' and `z'.  If C is not one of these characters,
the behaviour of `_toupper' is undefined.
*Portability*
`toupper' is ANSI C.  `_toupper' is not recommended for portable
programs.
   No supporting OS subroutines are required.